The ratio of para-/ortho-isomers in the synthesis of hydroxybenzyl alcohols comprising reacting a phenol with formaldehyde in the presence of a base catalyst is generally in the range of 1.0 or less. Thus, the main product of the reaction should be an o-hydroxybenzyl alcohol, and many reports have been presented with reference to the process for selectively preparing the o-isomer for the purpose of promoting the formation thereof.
On the other hand, since p-hydroxybenzyl alcohol is a useful compound as described above, some methods for increasing the product ratio have also been proposed. For example, there are known two methods, (1) a method for reacting phenol with paraformaldehyde in the presence of a strong basic catalyst and a polyalkylene ether (Japanese Patent Laid-Open Publication No. 141423/1980), and (2) a method for reacting phenol with paraformaldehyde in the presence of an organic nitrogen compound containing two or more nitrogen atoms in the molecule as a basic catalyst. However, as far as the present inventor knows, the content of the p-isomer in the mixture of hydroxybenzyl alcohols are 49% and 47%, respectively, in these methods, and thus the ratio of the p-/o-isomers still remains in the range no higher than 1.
Very recently, there has been reported a method for selectively synthesizing p-hydroxybenzyl alcohol with the use of cyclodextrin and substituted cyclodextrins (J. Chem. Soc., Chem. Commun., 652, 1988). This method, however, requires .beta.-cyclodextrin, sodium hydroxide and formaldehyde in proportions of 20 to 40, of 50 and of 40, respectively, to the amount of phenol as a raw material, so that it can scarcely be said to be an industrial method in view of the cost notwithstanding its high selectivity as the ratio of the p-/o-isomers is 15.7.
Japanese Patent Laid-Open Publication No. 106833/1989 also discloses as a method for selectively hydroxymethylating the p-position of a substituted phenol a method for selectively synthesizing a phenol with the use of cyclodextrin and substituted cyclodextrin. This method also has drawbacks in that it requires catalysts such as cyclodextrin and sodium hydroxide in excessive amounts to the substituted phenol and has a low reaction velocity, so that it may be difficult to employ the method in an industrial scale in consideration of its economy.